dt-bindings: interrupt-controller: aspeed: Add AST2700 SCU IC compatibles

Add compatible strings for the four SCU interrupt controller instances
on the AST2700 SoC (scu-ic0 to 3), following the multi-instance model used
on AST2600.

Also define interrupt indices in the binding header.

Signed-off-by: Ryan Chen <ryan_chen@aspeedtech.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/all/20250908011812.1033858-4-ryan_chen@aspeedtech.com